1. Field of the Invention
The present invention relates to a seal device of the non-contact type used for rotary air machines such as a turbine, blower and compressor to limit the amount of liquid leaked through those faces which are perpendicular to a rotating axis. More particularly, it relates to a seal device of the non-contact type which is held by a casing, wherein seal faces of the non-contact type are formed by an end face of a seal ring perpendicular to the axis of a rotating shaft and rotatable together with the rotating shaft and an end face of a stationary ring also perpendicular to the axis of the rotating shaft.
2. Prior Art
FIG. 8 shows a typical one of the conventional seal devices of the above noted non-contact type. In the case of this conventional seal device, dynamic pressure generating grooves 82 are formed in a seal face 81a of a rotating seal ring 81, extending at a certain interval along the circumferential direction of the seal face 81a. When the rotating seal ring 81 is rotated, sealed liquid is forceably taken in between the seal faces by the pumping action of the grooves 82 in the seal face 81a, so that a gap is formed between the seal faces, which are opposed to each other, to keep them out of contact.
In the case of this conventional seal device, however, it is difficult to keep the seal faces stably parallel to each other so as to produce excellent sealing capacity when the seal device is operated at high speed and under high pressure in the gas turbine, compressor or others. In other words, when the seal faces are distorted by pressure and heat they partly contact each other, because the gap between them is small. The distribution of pressures exerted on the seal faces is thus made unbalanced and they are therefore increasingly heated and develop distortions. They are thus damaged and are not able to produce any sealing capacity.
In order to solve this problem, Japanese Patent Publication Hei 1-22509 discloses another seal device wherein a rotating seal ring and a stationary ring are designed to have self aligning seal faces. In this seal device, three parameters such as the depth of each of the grooves in the seal face, the ratio at which the width of the seal face relative to the width of the groove in the radial direction of the seal face and the balance ratio are set in such a manner that, when the seal faces are to be distorted, a moment is automatically provided to prevent the seal faces from being distorted and keep them parallel to each other.
In the seal device disclosed in Japanese Patent Publication Hei 1-22509 having self aligning seal faces has its limits, however, because the values of the three parameters have limits. When the machine is not operated, therefore, the seal faces contact each other, but when the machine is operating, dynamic pressure is created to promote the leakage of sealed liquid. This increases the amount of liquid leaked.